Neisseria gonorrhoeae is the causative agent of the sexually transmitted infection gonorrhea. Genital gonorrhea is common in both genders, but has significant morbidity for women who are more frequently asymptomatically infected. Gonococcal infection in women has a range of symptoms that starts with dysuria and discharge and can end in conditions including pelvic inflammatory disease, internal abscess, ectopic pregnancy, or infertility. Infected individuals do not develop protective immunity, and the bacteria are rapidly developing antibiotic resistance. It is conceivable that soon we will not have an effective way to treat gonococcal infection. This issue has resulted in an increased incentive to develop a vaccine to prevent gonococcal disease. This study seeks to add to the field by exploring gonococcal properties that can be exploited for human vaccines or therapies. Interestingly, this pathogen has evolved to exclusively infect humans. In so doing, it has adapted unique methods of obtaining nutrients, including hijacking human proteins to acquire the essential nutrient iron. The gonococcal transferrin-iron acquisition system is composed of an integral, outer-membrane, TonB dependent transporter (TbpA), and a surface exposed lipo-protein (TbpB). This system is an ideal target for vaccine and drug development because it is plays a role in bacterial essential nutrient uptake, it is surface exposed, and the protein sequences are well conserved across strains. Previous studies have shown that gonococci lacking the transferrin iron acquisition system are incapable of initiating infection in human males. In addition, whole protein and epitope specific vaccine formulations derived from these proteins have shown growth inhibitory and bactericidal properties. Recently, crystal structures have been solved for TbpA and TbpB from the closely related pathogen Neisseria meningitidis. With a high level of sequence conservation between these two species, these crystals have been used to predict the three dimensional structure for the gonococcal proteins. This new information dramatically enhances the ability to target Tbp functional domains, which has significantly moved this field forward. This study will employ site specific mutagenesis of surface exposed loops of TbpA to assess key structure- function relationships in its interactions with human transferrin. In addition, several surface exposed loop peptides will be synthesized and will be used to immunize mice. The original peptides and the resulting sera will independently be characterized for their ability to interfere with TbpA-transferrin interactions. The goals of this study are to contribute to the understanding of how this receptor complex functions and to determine optimal targets for vaccine and drug development, such that new therapies can be developed for gonococcal infection before current treatments are rendered obsolete by acquired antibiotic resistance.